blk_mq_rq_from_pdu(9)

✨ blk_mq_rq_from_pdu ✨

okay bestie, welcome to the blk_mq_rq_from_pdu(9) page from the Kernel API Manual 💅 this one is short and sweet and honestly kind of iconic — it's the little reverse-magic trick where you get your request back out of a PDU 🎀

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🌸 NAME 🌸

blk_mq_rq_from_pdu — cast a PDU to a request ✨

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🦋 SYNOPSIS 🦋

struct request * blk_mq_rq_from_pdu (void *pdu );

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💖 ARGUMENTS 💖

• pdu — the PDU (Protocol Data Unit) to be casted 🫶 this is the thing you're handing over so it can get turned back into a request

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⭐ RETURN ⭐

request — that's what you get back, no cap 💅

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👑 DESCRIPTION 👑

so here's the vibe check: driver command data is immediately after the request. literally right behind it, following it in memory 🧚

so to get back to the original request, you subtract the request size. that's it. that's the whole trick. math but make it slay 🔥

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/blk-mq.h 📁
• enum blk_eh_timer_return(9)
• struct blk_mq_hw_ctx(9)
• struct blk_mq_queue_map(9)
• enum hctx_type(9)
• struct blk_mq_tag_set(9)
• struct blk_mq_queue_data(9)
• struct blk_mq_ops(9)
• blk_mq_rq_state(9)
• blk_mq_add_to_batch(9)
• blk_mq_rq_to_pdu(9)
• blk_rq_nr_bvec(9)
• blk_rq_passthrough_stats(9)

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lowkey the whole page is like six lines and I'm obsessed with it for that 🙈 go read the friends listed above if you want the full lore, iykyk 💜

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and that's the whole thing bestie!! 🍓 this little cutie lives in ./include/linux and the page is dated October 2026 — signed off with love by blk_mq_rq_from_pdu(9) herself 💌 ✨🎀